Condensation of exciton-polaritons in semiconductor microcavities takes place despite in plane disorder. Below the critical density the inhomogeneity of the potential seen by the polaritons strongly limits the spatial extension of the ground state. This limitation can be overcome above the critical density thanks to a non linear coupling, resulting in a mode locking effect. This is clearly evidenced by spatial and spectral studies, coupled to interferometric measurements. In case of strong disorder, several non mode-locked independent condensates can be evidenced, which present accordingly the expected lack of phase locking. The transition from dependent to independent condensates is addressed considering multiple realizations of the disorder.